Tube heat exchanger with anti-freeze thermostat

ABSTRACT

1,102,277. Air heaters. SVENSKA FL€KTFABRIKEN A.B. 10 May, 1965 [11 May, 1964], No. 19646/65. Heading F4S. In a tubular heat exchanger in which outdoor air is heated in passing over hot water tubes 2 (arrows A-B), means for preventing freeze-up of the tubes under conditions of low outdoor air temperature comprise a thermostat 5, 6, 7 associated with manoeuvering means (not shown) for either shutting off the outdoor air stream from the heat exchanger, or for mixing room air with the air stream passing to the heat exchanger, the temperature sensing part 5 of the thermostat being located in an active part of the heat exchanger (e.g. the lowest tube 2) close to the water outlet 4. This temperature sensing part 5 is of a diameter such as to ensure that the volumetric flow in the tube portion surrounding said part is less than the flow in the other tubes 2 of the heat exchanger.

Nov. 28, 1967 LARs-OWE GRUDEBORN 3,354,945'

TUBE HEAT EXCHANGER WITH ANTl-FREEZE THERMOSTAT Filed March 29, 1967 F'IGQ.

INVENTOR: GRUDEBORN BY LARS-OWE AT TYS .Y

United States Patent Giice 3,354,945 TUBE HEAT EXCHANGER WITH ANTI-FREEZE THERMOSTAT Lars-Owe Grudeborn, Jonkoping, Sweden, assignor t Aktiebolaget Svenska Flaktfabriken, Stockholm, Sweden Filed Mar. 29, 1967, Ser. No. 626,817 Claims priority, application Sweden, May 11, 1964, 5,707/ 64 2 Claims. (Cl. 165-40) ABSTRACT 0F THE DISCLOSURE In a tube heat exchanger for heating outdoor air by means of hot Water flowing through the tubes thereof, a thermostat mounted within one of the tubes having associated therewith control means for reducing the cooling elfect of the outdoor air flowing through the heat exchanger when there is a risk of freezing.

The present aplication is a continuation-impart of my copending application Ser. No. 454,787 tiled May l1, 1965 and now abandoned.

The present invention relates to tube heat exchangers for heating outdoor air by means of hot Water and more particularly to a device for preventing freezing of the water in the exchanger.

Heat exchangers used for heating outdoor air by means of hot water are subject to freezing in many climatic zones in winter. In order to eliminate the risk of freezing, heat exchangers have been equipped with an antifreeze thermostat which operates to reduce the flow of outside air. The sensing body of the thermostat is placed in the path of the air in close contact with the tubes of the heat exchanger 'or is placed in the return pipe for water outside the heat exchanger. These two arrangements have also been combined. In the first case, however, the sensing body senses primarily a temperature which falls between the temperatures of the outdoor air and that of the water (i.e., a temperature below that of the water), and the sensing body must therefore be located on the rear side of the heat exchanger in the path of flow of the air so as not to give an impulse before a real risk of freezing occurs. In spite of this, with arrangements of this type, it is not possible to eliminate completely the risk of interruptions in the flow of the outdoor air caused by improper impulses on occasions when no reak risk of freezing exists. In the second case, where the sensing body is located in the return pipe outside of the heat exchanger, the tute heat exchanger may be damaged Iby freezing if the ow of water through the heat exchanger is interrupted, since the sensing body cannot possibly sense the temperature drop in the water which remains in the heat exchanger.

The present invention eliminates the drawbacks of the aforementioned arrangements by providing a thermostat having a sensing body mounted in the heat exchanger itself so as to be sensitive to the water flow within the active part of the heat exchanger.

In accordance with a feature of the invention, the sensing body of the thermostat is made with a cross section which is sufficiently small relative to the cross sectional area of the tube of the heat exchanger so that the free ow area for the Water, in the area where the sensing element is mounted, is small so as not to reduce the free ilow area in that tube more than necessary, to insure that the volumetric rate of Water flow in the tube having the sensing element is less than in the remaining tubes of the heat exchanger.

All of the objects of the invention are more fully set forth hereinafter with reference to the accompanying drawing, wherein:

3,354,945 Patented Nov. 28, 1967 FIG. 1 is a fragmentary perspective view of a heat exchanger embodying an anti-freeze thermostat in accordance with the present invention;

FIG. 2 is a diagrammatic view illustrating the preferred environment for the heat exchanger of FIG. 1 in accordance with the present invention;

Referring now to FIG. l, the tube heat exchanger comprises a casing 1 having a series of finned tubes 2 connected at one side to a common header 3 which is connected with a return pipe 4 for the hot water flowing through the heat exchanger. A similar header (not shown) is connected to the tubes 2 at the other side for supplying hot water to the tubes from a hot water supply pipe 11 (FIG. 2). As shown in FIG. 2, the casing is mounted in a duct 12 adapted to receive outside air, for example through a conduit 13 having a damper 14 therein. Secondary room air may be supplied to the duct 12 by means of a conduit 15 having a similar damper 16 therein. The outside air from the duct 12 is caused to flow through the heat exchanger 1 by means of a blower 17 having suitable control means 18. The dampers 14 and 16 may be controlled automatically by a controller 19 and normally the dampers are set to provide full ilow through the conduit 13 and minimum ow through the conaduit 15, so as to supply maximum outside air to the warmed-air room inlet 20.

In accordance with the invention, a thermostat is provided which is responsive to the temperature of the water flowing through the tubes of the heat exchanger close to and upstream of the water return pipe 4. To this end, a thermostat 7 is provided having a capillary tube 6 connected to a sensing element 5 which is positioned in the tube 2 which is closest to the return duct 4. The cross sectional area of the sensing element 5 relative to the cross sectional area of the tube Z is small so as not to reduce the free flow area for the water in the tube more than necessary, to insure that the volumetric flow in the tube having the sensing element 5 is less than the ow in the remaining tubes of the heat exchanger. Because of this relationship, the Water in the tube having the sensing element therein will be cooled to a greater extent than the water in the remaining tubes and will therefore provide a proper reading in the thermostat 7 to prevent freezing in any of the tubes of the heat exchanger. The thermostat 7, when its reading indicates a freeze is likely to occur, is connected to the controls 18 and 19, as desired, either to reduce the total ow of cold air through the exchanger, or to introduce warmer air into the flow of cold air so as to moderate or reduce the cooling effect of the air flow upon the water in the tube heat exchanger. It is preferred to reduce the cooling effect of the outdoor air rather than to increase the heating effect of the water since the water is normally supplied from a remote source which supplies hot water to a plurality of locations and which is not readily susceptible to regulation of its heating effect.

While a particular embodiment of the present invention has been herein illustrated and described, it is not intended to limit the invention to such disclosure, but changes and modifications may be made therein and thereto within the scope of the following claims.

I claim:

1. In a tubular heat exchanger for heating outdoor air having at least one tube connected at one end to a remote source supplying heated water and at the other end to a return pipe, an inlet for introducing outside air `to said heat exchanger and an outlet for discharging the 3 4 operating said control means including a sensing body in the volumetric flow in said tube is less than in the remainsaifl tube itl. the flow-path of the Water .C1956 t9 and infubesofsad heatexchange l upstream of the Water return pipe.

2. A tubular heat exchanger according to claim 1 in- References Cited cluding a plurality of tubes connected in parallel between 5 UNITED STATES PATENTS common headers, said sensing element being mounted in 1,942,559 1/1934 Lithman 219-341 one of said tubes, the cross sectional area of said sensing 2,190,232 2/ 1950 Fry 16S-39 body relative to the cross sectional area of said tube being small so as not to reduce the free flow area for the ROBERT A O LEARY Pnmary Examiner' water in said tube more than necessary, to insure that 10 CHARLES SUKALO, Examiner. 

1. IN A TUBULAR HEAT EXCHANGER FOR HEATING OUTDOOR AIR HAVING A LEAST ONE TUBE CONNECTED AT ONE END TO A REMOTE SORUCE SUPPLYING HEATED WATER AND AT THE OTHER END TO A RETURN PIPE, AND INLET FOR INTRODUCING OUTSIDE AIR TO SAID HEAT EXCHANGER AND AN OUTLET FOR DISCHARGING THE HEATED OUTDOOR AIR FROM SAID HEAT EXCHANGER, SAID INLET HAVING CONTROL MEANS FOR REDUCING THE COOLING EFFECT OF OUTDOOR AIR UPON THE WATER FLOWING THROUGH SAID TUBE; THE IMPROVEMENT COMPRISING AN ANTIFREEZE THREMOSTAT FOR OPERATING SAID CONTROL MEANS INCLUDING A SENSING BODY IN SAID TUBE IN THE FLOW PATH OF THE WATER CLOSE TO AND UPSTREAM OF THE WATER RETURN PIPE. 